This invention relates to a device and method for warming inlet air for a massecuite separating centrifuge. In currently available separating systems, the centrifuge capacity and the purity of the separated sugar are limited by the high viscosity of the massecuite processed. In the normal massecuite separation temperature range of 45.degree.-55.degree. C, the viscosity of the massecuite varies greatly with temperature. It is advantageous to process the massecuite at the highest possible temperature, since the throughput per square inch of screen at constant G-factor is higher when the massecuite viscosity is low. In addition, processing at lower viscosities results in faster, more complete drainage of the liquid. This enables dryer, less colored sugar crystals to be obtained. However, the massecuite inlet temperature must be kept below the temperature at which the sugar crystals begin to melt. When massecuite has been heated below this melting temperature and the feed directed into a conventional centrifugation system, it has been found that the massecuite is cooled substantially below the desired separation temperature by the cold air drawn into the centrifuge basket.
In prior art systems, hot air blowers or electric heaters have been employed in the centrifugal inlet to warm the ambient air to the centrifuge. However, the operating costs of these units tend to be high. Other systems designed for raising air and massecuite temperature have involved spraying steam directly onto the massecuite or installing complex heating devices. Directing steam onto the outer periphery of massecuite supply as it enters the centrifugal is not desirable, since steam may melt the outer sugar crystals in the massecuite, while not heating the inner massecuite sufficiently. The complex heating devices employed usually have proven expensive to manufacture, operate and clean. Moreover, some of the devices restrict the opening into the centrifuge, thereby raising the possibility of pluggage at the centrifuge inlet if the inlet massecuite stream contacts and adheres to the heating devices. This would cause back-ups in the massecuite supply system and also result in interruptions in the flow of massecuite to the centrifuge basket.
An object of this invention is to provide a device and system for warming the air surrounding the inlet massecuite, to thereby maintain the massecuite at temperatures more favorable for separation without melting the outer exposed sugar crystals.
A further object is to provide an air warming member with a relatively non-restricted opening above the centrifuge in which the inner surface is heated to prevent or minimize the effect of massecuite sticking to the member surface.
Another object is to provide a system for continuously warming the elements of a rotating massecuite separating centrifuge which contact the massecuite, to thereby add additional heat to the massecuite.
In the present invention, the aforementioned objects are accomplished by the utilization above the centrifuge basket of a plurality of tubular members which form a chamber having a plurality of inwardly directed nozzles communicating with a source of steam, or similar heat transfer fluid, which discharge in a vortex type flow the heated fluid around massecuite passing through the members into the centrifuge. In the preferred embodiment, steam is directed into a chamber formed between a pair of nested, concentric, frusto-conical members. The steam is then discharged through a plurality of uniformly distributed, inwardly directed nozzles in the conical wall of the inner member. The nozzles are directed substantially tangentially and slightly downwardly creating a vortex of steam and air around the inlet massecuite stream to prevent excessive cooling of the massecuite during subsequent processing, without substantial quantities of the steam directly contacting the massecuite and possibly scorching or melting the sugar crystals therein. This mixture of steam and warmed air is then drawn into the centrifuge basket, where it continues to warm the massecuite while also heating the centrifuge basket screen and accelerator bell. These centrifuge elements, in turn, transmit a portion of this heat to the massecuite on contact. With this design, the opening into the centrifuge basket is not significantly restricted by the nozzles, resulting in little, if any, massecuite contacting the inner member surface. Since steam flow in the chamber formed between the members heats the surface of the inner member, any massecuite accidentally sticking to this surface is quickly melted and slides into the centrifuge basket.